During hypo- and hyperbaric decompression, gas-supersaturation of blood and tissues can cause bubbles to form with serious medical consequences. The object of the present study is to increase the understanding of the early etiology of the air embolism, since essential information is lacking as to where and how the bubbles form, and the physical factors which affect this process. Several aspects of the gas bubble nucleation process will be investigated in cells and other components of the blood in vitro, in some unicellular organisms, and in various liquid-liquid and liquid-solid interface model systems. It is of particular interest to determine the gas supersaturations that are required for the spontanous nucleation of bubbles in both intact and injured cells, and to identify the intracellular component (s) of lowest cavitation stability. The methods to be used for this will include an especially developed cinemicrographic technique which allows gas-supersaturated cell suspensions to be monitored during decompression at 650 X magnification and a film speed of 2 to 200 frames per second. Other experiments will be carried out on solutions containg various types of crystals under gas-supersaturated conditions in order to assess the effect which solid interfaces has on the nucleon process. Liquid-liquid interfaces of hydrophobic nature will similarly be examined, using suspensions and emulsions. Also, in order to perform some more quantitative and theoretical treatments of the data obtained so far it will be necessary to determine the solubilities of gases in various liquids at elevated pressures. A method for this has been developed to yield the necessary precision of plus or minus 1 percent in the solubility coefficients.